The present invention is specific to an improved capacitor and method of making an improved capacitor. More specifically, the present invention is directed to a method of manufacturing a hermetically sealed capacitor with improved performance.
Hermetically sealed capacitors have found widespread use in applications where environmental conditions are detrimental to capacitor performance. In general, a hermetically sealed capacitor comprises a capacitive element comprising a valve metal anode with a dielectric thereon and a conductive layer on the dielectric. The capacitive element is then hermetically sealed in a casing. Whereas wet type hermetically sealed capacitors utilize an electrolyte solution as the cathode conductor, hermetically sealed solid electrolytic capacitors use a solid conductor, such as MnO2 or intrinsically conducting polymer, as the cathode conductor. In recent years intrinsically conductive polymers such as poly 3,4-ethylenedioxythiophene (PEDT) have been used as the preferred cathode conductor in electrolytic capacitors due, in part, to their high electrical conductivity and benign failure mode. Capacitors made using in-situ oxidative polymerization or electrochemical polymerization have high DC leakage current and have been limited to use in capacitors intended for applications at lower working voltage. U.S. Pat. No. 7,563,290, which is incorporated herein by reference, describes a method of improving the working voltage of solid electrolytic capacitors by dispersion of prepolymerized conductive polymers.
There has been a long felt desire for improved hermetically sealed capacitors. In particular, there has been a long felt desire for hermetically sealed solid electrolytic capacitors with lower leakage current and good reliability during the useful life of the capacitor.